Dr. Sears has some great suggestions on weaning here at his site

www.askdrsears.com/html/2/T026400.asp

I am not near ready to wean my daughter at 21 months, but I remember my mom weaning my youngest brother (about the same age as your daughter) and she sat him down and did the "big boy" talk with him. And told him big boys didn't have "these" anymore and he said ok and that was the end of it. I think as kids get older and understand more you can just talk them through the process a little easier than just taking away.

My oldest daughter was (dare I admit it?) almost four before she was ready to give up her night-time nurse; in the end we did have the "you're a big girl now," talk; I've heard people recommend a "weaning day" present, too. I think it's almost harder to break off once it's down to a habit and part of a routine, like bedtime (or your daugher's midday ritual).

Just for a flip perspective, my mother nursed my brother and I until we were four, too, and I a) have no recollection of it, and b) we both have actually turned out to be reasonably well adjusted and healthy adults---so don't worry too much, your daughter will be just fine either way. And she really WON"T nurse until college... it only feels that way. :)

I think (from my rather un-scientific survey of traditional cultures in first-year anthropology class) that typical "traditional" weaning ages tend to be anywhere between two and four years. On the other hand, in most primates weaning correlates with with the eruption of the first adult molars (which in humans occurs around age 6). (No, I'm not suggesting we should be still nursing our first-graders, but it's an interesting tidbit nonetheless).